FIGS. 1-4, inclusive, illustrate prior art systems.
FIG. 1 is a schematic illustration of a typical power conversion system 20. Aerodynamic rotor 22 is connected via rotating shaft 24 to speed increaser gear box 26. Aerodynamic rotor 22 typically operates at a rotational speed in the range of 20 to 300 rpms. Gear box 26 translates the rotational speed of shaft 24 into a relatively higher rotational speed of shaft 28, which in turn is connected to conventional generator 30. Power electronic control 32 is sometimes used to control the generator and to convert the generator's variable-voltage, variable-frequency power to a standard utility voltage and frequency. Utility grid 34 receives and stores the generator electricity for use.
Aerodynamic rotor 22 is usually a propeller-type rotor, such as rotor 40 in FIGS. 2 and (3). A plural of blades 42 are connected to and extend radially out from central hub 44. Hub 44 is connected to a distal end of shaft 46 which rotates with hub 44 and blades 42 in response to wind W impinging on blades 42. FIG. 3 shows a front view of aerodynamic rotor 40 which optimally would receive wind from a direction normal to the plane of the figure.
There are two common types of speed increasers that are used in wind turbines, a gear box and a belt-and-pulley transmission. A speed increaser is required because there is a mismatch between the optimally-efficient operating speed of the aerodynamic rotor and the electric generator. The most efficient conversion speeds of most aerodynamic rotors are typically much lower than the optimally-efficient, rotational speeds of standard industrial electric machines such as squirrel-cage induction or synchronous generators. These machines are designed for relatively high-speed, low-torque operation. For example, the standard four-pole induction or synchronous machine operates at 60 Hz at a nominal speed of 1800 rpm. In contrast, depending on the power level of the aerodynamic rotor operating in air, the aerodynamic rotor may have an operating speed in the range of 20 rpm to 300 rpm. Depending on the wind speed regime, the 20 rpm speed may apply to rotors designed to deliver 600 kW to 1000 kW of shaft power. Similarly, the 300 rpm speed might apply to much smaller rotors designed to deliver 2 kW to 10 kW. Use of a speed increaser significantly increases the number of required parts, cost of manufacturing, complexity of ultimate design and potential for mechanical failure. Use of a speed increaser also results in a loss of power conversion efficiency.
Wind turbines have been manufactured which do not require speed increasers to translate shaft rotational speed between an aerodynamic rotor and a generator. Such systems are referred to as "direct-drive wind turbines." For example, as shown in FIG. 4, power conversion system 70 employs a propeller-type aerodynamic rotor 72 connected via rotary shaft 74 to direct drive generator 76. Shaft 74 rotates with rotor 72. Shaft 74 is supported by bearings (not shown). The main shaft support bearings can be located on the shaft in a pillow-block arrangement or can be located within the gear box. Power conversion system 70 is a variable-speed configuration which employs power electronic control 78 to control the generator and to convert the generator's variable-voltage, variable-frequency power to a standard utility voltage and frequency.
An object of the invention is to provide a simple, manufacturable and efficient system for interconverting moving fluid power and electrical power.
A more specific object of the invention is to efficiently convert fluctuating wind power into electricity.
Another object of the invention is to provide a wind turbine which does not require a speed-increaser to couple the torque and power from an aerodynamic rotor to an electric machine.
Still another object of the invention is to employ a shaft and support bearing configuration for an aerodynamic rotor which eliminates the fluctuating bending moments which occur when a shaft is required to support and rotate with an aerodynamic rotor.